In an image capture system an image scanner is used to scan a document and convert the document image to digital signals that can then be transmitted to a computer for processing. In digital form the document image can be readily stored, retrieved, duplicated and transmitted. Image capture systems are being used to provide high-speed processing of the growing quantities of information generated by modern society.
A typical image capture apparatus is equipped with a document transport apparatus that transports documents to a scanning section. It is also equipped with a document feeder that draws documents from a stack arranged in a document feed tray and feeds the documents one at a time at prescribed intervals to the document transport apparatus. In the document feeder, a counterclockwise rotation of a feed roller feeds a topmost document in the direction of the document transport apparatus. At the same time a counterclockwise rotation of a retard roller positioned below the feed roller serves to urge the documents below the topmost one back towards the document feed tray. In this way, documents are supplied separately one by one to the document transport apparatus which transports them to an image capture section where they are scanned.
To improve the efficiency of this scanning operation, the space between documents is made as small as possible., while at the same time document transport speeds are made as high as possible. Additionally, with the aim of decreasing the size of the apparatus, curved transport paths are used. This combination of factors leads to various problems. For example, unstable transport speeds result from slippage between documents and the surface of the conveying means. These unstable speeds and other such problems cause documents to overlap. After documents become overlapped, they are typically transported in that state.
At the scanning section such overlapped documents may be judged to be a single long document, resulting in these overlapped documents being incorrectly scanned. Because an image capture apparatus continues to operate normally as long as documents do not jam or other such operational malfunctions occur, it has been extremely difficult to detect such mis-scanned documents among a large number of documents being processed at high speed.
It is therefore desirable to provide a document transport apparatus that reacts immediately to overlapped documents so that any mis-scanning can be avoided or corrected.